The present invention relates to a toner used for developing electrostatic images in an image forming method, such as electrophotography or electrostatic recording, or for use in an image forming method according to the toner jetting scheme.
Hitherto, a large number of electrophotographic processes have been known, as disclosed in, e.g., U.S. Pat. Nos. 2,297,691, 3,666,363 and 4,071,361. In these processes, an electrostatic image is formed on a photosensitive member comprising generally a photoconductive material by various means, then the electrostatic image is developed with a toner, and the resultant toner image is, after being transferred onto a transfer(-receiving) material such as paper via or without via an intermediate transfer member, fixed by heating, pressing, heating and pressing, or with solvent vapor, to obtain a copy or a print. A transfer residual toner remaining on the photosensitive member after the transfer step is cleaned by various means, and the above-mentioned steps are repeated for a subsequent image forming cycle.
A toner has to be provided with a positive or a negative charge depending on the polarity of an electrostatic latent image to be developed therewith. A toner can be provided with a charge by utilizing the triboelectric chargeability of a resin as a toner component, but the chargeability obtained only by this measure is unstable, so that the toner image density cannot be raised quickly at an initial stage from start-up of image formation and the resultant images are liable to be foggy. Accordingly, in order to provide a toner with a desired triboelectric chargeability, it has been generally practiced to add a charge control agent to the toner.
Examples of negative chargeability-imparting charge control agents known at present may include: metal complex salts of monoazo dyes; metal complex salts of hydroxycarboxylic acids, dicarboxylic acids and aromatic diols; and resins containing acid components. On the other hand, examples of positive chargeability-imparting agents may include: nigrosine dyes, azine dyes, triphenylmethane dyes and pigments, quaternary ammonium salts, and polymers having a branch of quaternary ammonium salt.
However, many of metal complexes of azo dye structure used as charge control agents generally lack a stability and are liable to lose their initial charge control performance by decomposition or denaturation when subjected to mechanical friction or impact, change in temperature or humidity, electrical impact, or exposure to light. Further, some of them having a practical level of charge-imparting ability can be problematic in charge stability or contain much impurity chemicals lacking charge controlling effect due to fluctuation in production conditions, thus leaving problems in respects of stability and reliability of their performance.
For example, a monoazo dye metal complex disclosed in Japanese Laid-Open Patent Application (JP-A) 9-169919 is excellent in triboelectric charge-imparting performance but is still insufficient in providing stable developing performance regardless of environmental change, continual use and other conditions of use.
JP-A 11-7164 discloses an amorphous metal complex salt comprising a monoazo compound as a ligand for a charge control agent and also discloses alkyl group-containing monoazo compounds as examples. However, the JP reference does not disclose specific examples of producing a toner containing a metal complex salt including a ligand of such an alkyl group-containing monoazo compound as a charge control agent and does not pay consideration to a relationship between the charge control agent and a toner resin component. Further, such an amorphous metal complex is excellent in dispersibility in toner and charge-imparting performance but is liable to cause toner sticking onto the photosensitive member and gradual decrease in developing performance due to toner degradation in long-term use of the toner because it is relatively soft.
Accordingly, a generic object of the present invention is to provide a toner having solved the above-mentioned problems.
A more specific object of the present invention is to provide a toner capable of exhibiting excellent low-temperature fixability and anti-offset property even at a high process speed.
Another object of the present invention is to provide a toner capable of forming high-resolution and high-definition images.
Another object of the present invention is to provide a toner comprising toner particles wherein respective components are uniformly dispersed, and thus being capable of providing excellent images even in a long-term of use similarly as in the initial stage.
A further object of the present invention is to provide a toner excellent in long-term storability and environmental stability.
According to the present invention, there is provided a toner comprising toner particles each comprising a binder resin, a colorant and an organometallic compound, wherein
the organometallic compound is an azo iron compound formed from a monoazo compound having at least one alkyl group and two hydroxyl groups capable of bonding with an iron atom, and
the toner has a tetrahydrofuran-soluble content providing a gel-permeation chromatogram showing at least one peak in a molecular weight region of 3xc3x97103 to 5xc3x97104 and at least one peak or shoulder in a molecular weight region of above 5xc3x97104 and at most 1xc3x97107.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.